我将学习OpenCL，并希望从容易开始。
我找到并修改了这个hello world示例abit但没什么必要的。 http://developer.apple.com/library/mac/#samplecode/OpenCL_Hello_World_Example/Introduction/Intro.html
//
// File: hello.c
//
// Abstract: A simple "Hello World" compute example showing basic usage of OpenCL which
// calculates the mathematical square (X[i] = pow(X[i],2)) for a buffer of
// floating point values.
//
//
// Version: <1.0>
//
// Disclaimer: IMPORTANT: This Apple software is supplied to you by Apple Inc. ("Apple")
// in consideration of your agreement to the following terms, and your use,
// installation, modification or redistribution of this Apple software
// constitutes acceptance of these terms. If you do not agree with these
// terms, please do not use, install, modify or redistribute this Apple
// software.
//
// In consideration of your agreement to abide by the following terms, and
// subject to these terms, Apple grants you a personal, non - exclusive
// license, under Apple's copyrights in this original Apple software ( the
// "Apple Software" ), to use, reproduce, modify and redistribute the Apple
// Software, with or without modifications, in source and / or binary forms;
// provided that if you redistribute the Apple Software in its entirety and
// without modifications, you must retain this notice and the following text
// and disclaimers in all such redistributions of the Apple Software. Neither
// the name, trademarks, service marks or logos of Apple Inc. may be used to
// endorse or promote products derived from the Apple Software without specific
// prior written permission from Apple. Except as expressly stated in this
// notice, no other rights or licenses, express or implied, are granted by
// Apple herein, including but not limited to any patent rights that may be
// infringed by your derivative works or by other works in which the Apple
// Software may be incorporated.
//
// The Apple Software is provided by Apple on an "AS IS" basis. APPLE MAKES NO
// WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION THE IMPLIED
// WARRANTIES OF NON - INFRINGEMENT, MERCHANTABILITY AND FITNESS FOR A
// PARTICULAR PURPOSE, REGARDING THE APPLE SOFTWARE OR ITS USE AND OPERATION
// ALONE OR IN COMBINATION WITH YOUR PRODUCTS.
//
// IN NO EVENT SHALL APPLE BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL OR
// CONSEQUENTIAL DAMAGES ( INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION ) ARISING IN ANY WAY OUT OF THE USE, REPRODUCTION, MODIFICATION
// AND / OR DISTRIBUTION OF THE APPLE SOFTWARE, HOWEVER CAUSED AND WHETHER
// UNDER THEORY OF CONTRACT, TORT ( INCLUDING NEGLIGENCE ), STRICT LIABILITY OR
// OTHERWISE, EVEN IF APPLE HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Copyright ( C ) 2008 Apple Inc. All Rights Reserved.
//
////////////////////////////////////////////////////////////////////////////////
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
//#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <CL/opencl.h>
#define Warning(...) fprintf(stderr, __VA_ARGS__)
////////////////////////////////////////////////////////////////////////////////
// Use a static data size for simplicity
//
#define DATA_SIZE (1024)
////////////////////////////////////////////////////////////////////////////////
// Simple compute kernel which computes the square of an input array
//
const char *KernelSource = "\n" \
"__kernel void square( \n" \
" __global float* input, \n" \
" __global float* output, \n" \
" const unsigned int count) \n" \
"{ \n" \
" int i = get_global_id(0); \n" \
" if(i < count) \n" \
" output[i] = input[i] * input[i]; \n" \
"} \n" \
"\n";
////////////////////////////////////////////////////////////////////////////////
/*
* CLErrString --
*
* Utility function that converts an OpenCL status into a human
* readable string.
*
* Results:
* const char * pointer to a static string.
*/
static const char *
CLErrString(cl_int status) {
static struct { cl_int code; const char *msg; } error_table[] = {
{ CL_SUCCESS, "success" },
{ CL_DEVICE_NOT_FOUND, "device not found", },
{ CL_DEVICE_NOT_AVAILABLE, "device not available", },
{ CL_COMPILER_NOT_AVAILABLE, "compiler not available", },
{ CL_MEM_OBJECT_ALLOCATION_FAILURE, "mem object allocation failure", },
{ CL_OUT_OF_RESOURCES, "out of resources", },
{ CL_OUT_OF_HOST_MEMORY, "out of host memory", },
{ CL_PROFILING_INFO_NOT_AVAILABLE, "profiling not available", },
{ CL_MEM_COPY_OVERLAP, "memcopy overlaps", },
{ CL_IMAGE_FORMAT_MISMATCH, "image format mismatch", },
{ CL_IMAGE_FORMAT_NOT_SUPPORTED, "image format not supported", },
{ CL_BUILD_PROGRAM_FAILURE, "build program failed", },
{ CL_MAP_FAILURE, "map failed", },
{ CL_INVALID_VALUE, "invalid value", },
{ CL_INVALID_DEVICE_TYPE, "invalid device type", },
{ 0, NULL },
};
static char unknown[25];
int ii;
for (ii = 0; error_table[ii].msg != NULL; ii++) {
if (error_table[ii].code == status) {
return error_table[ii].msg;
}
}
_snprintf(unknown, sizeof unknown, "unknown error %d", status);
return unknown;
}
/*
* PrintDevice --
*
* Dumps everything about the given device ID.
*
* Results:
* void.
*/
static void
PrintDevice(cl_device_id device) {
#define LONG_PROPS \
defn(VENDOR_ID), \
defn(MAX_COMPUTE_UNITS), \
defn(MAX_WORK_ITEM_DIMENSIONS), \
defn(MAX_WORK_GROUP_SIZE), \
defn(PREFERRED_VECTOR_WIDTH_CHAR), \
defn(PREFERRED_VECTOR_WIDTH_SHORT), \
defn(PREFERRED_VECTOR_WIDTH_INT), \
defn(PREFERRED_VECTOR_WIDTH_LONG), \
defn(PREFERRED_VECTOR_WIDTH_FLOAT), \
defn(PREFERRED_VECTOR_WIDTH_DOUBLE), \
defn(MAX_CLOCK_FREQUENCY), \
defn(ADDRESS_BITS), \
defn(MAX_MEM_ALLOC_SIZE), \
defn(IMAGE_SUPPORT), \
defn(MAX_READ_IMAGE_ARGS), \
defn(MAX_WRITE_IMAGE_ARGS), \
defn(IMAGE2D_MAX_WIDTH), \
defn(IMAGE2D_MAX_HEIGHT), \
defn(IMAGE3D_MAX_WIDTH), \
defn(IMAGE3D_MAX_HEIGHT), \
defn(IMAGE3D_MAX_DEPTH), \
defn(MAX_SAMPLERS), \
defn(MAX_PARAMETER_SIZE), \
defn(MEM_BASE_ADDR_ALIGN), \
defn(MIN_DATA_TYPE_ALIGN_SIZE), \
defn(GLOBAL_MEM_CACHELINE_SIZE), \
defn(GLOBAL_MEM_CACHE_SIZE), \
defn(GLOBAL_MEM_SIZE), \
defn(MAX_CONSTANT_BUFFER_SIZE), \
defn(MAX_CONSTANT_ARGS), \
defn(LOCAL_MEM_SIZE), \
defn(ERROR_CORRECTION_SUPPORT), \
defn(PROFILING_TIMER_RESOLUTION), \
defn(ENDIAN_LITTLE), \
defn(AVAILABLE), \
defn(COMPILER_AVAILABLE),
#define STR_PROPS \
defn(NAME), \
defn(VENDOR), \
defn(PROFILE), \
defn(VERSION), \
defn(EXTENSIONS),
#define HEX_PROPS \
defn(SINGLE_FP_CONFIG), \
defn(QUEUE_PROPERTIES),
/* XXX For completeness, it'd be nice to dump this one, too. */
#define WEIRD_PROPS \
CL_DEVICE_MAX_WORK_ITEM_SIZES,
static struct { cl_device_info param; const char *name; } longProps[] = {
#define defn(X) { CL_DEVICE_##X, #X }
LONG_PROPS
#undef defn
{ 0, NULL },
};
static struct { cl_device_info param; const char *name; } hexProps[] = {
#define defn(X) { CL_DEVICE_##X, #X }
HEX_PROPS
#undef defn
{ 0, NULL },
};
static struct { cl_device_info param; const char *name; } strProps[] = {
#define defn(X) { CL_DEVICE_##X, #X }
STR_PROPS
#undef defn
{ CL_DRIVER_VERSION, "DRIVER_VERSION" },
{ 0, NULL },
};
cl_int status;
size_t size;
char buf[65536];
long long val; /* Avoids unpleasant surprises for some params */
int ii;
for (ii = 0; strProps[ii].name != NULL; ii++) {
status = clGetDeviceInfo(device, strProps[ii].param, sizeof buf, buf, &size);
if (status != CL_SUCCESS) {
Warning("\tdevice[%p]: Unable to get %s: %s!\n",
device, strProps[ii].name, CLErrString(status));
continue;
}
if (size > sizeof buf) {
Warning("\tdevice[%p]: Large %s (%d bytes)! Truncating to %d!\n",
device, strProps[ii].name, size, sizeof buf);
}
printf("\tdevice[%p]: %s: %s\n",
device, strProps[ii].name, buf);
}
printf("\n");
status = clGetDeviceInfo(device, CL_DEVICE_TYPE, sizeof val, &val, NULL);
if (status == CL_SUCCESS) {
printf("\tdevice[%p]: Type: ", device);
if (val & CL_DEVICE_TYPE_DEFAULT) {
val &= ~CL_DEVICE_TYPE_DEFAULT;
printf("Default ");
}
if (val & CL_DEVICE_TYPE_CPU) {
val &= ~CL_DEVICE_TYPE_CPU;
printf("CPU ");
}
if (val & CL_DEVICE_TYPE_GPU) {
val &= ~CL_DEVICE_TYPE_GPU;
printf("GPU ");
}
if (val & CL_DEVICE_TYPE_ACCELERATOR) {
val &= ~CL_DEVICE_TYPE_ACCELERATOR;
printf("Accelerator ");
}
if (val != 0) {
printf("Unknown (0x%llx) ", val);
}
printf("\n");
} else {
Warning("\tdevice[%p]: Unable to get TYPE: %s!\n",
device, CLErrString(status));
}
status = clGetDeviceInfo(device, CL_DEVICE_EXECUTION_CAPABILITIES,
sizeof val, &val, NULL);
if (status == CL_SUCCESS) {
printf("\tdevice[%p]: EXECUTION_CAPABILITIES: ", device);
if (val & CL_EXEC_KERNEL) {
val &= ~CL_EXEC_KERNEL;
printf("Kernel ");
}
if (val & CL_EXEC_NATIVE_KERNEL) {
val &= ~CL_EXEC_NATIVE_KERNEL;
printf("Native ");
}
if (val) {
printf("Unknown (0x%llx) ", val);
}
printf("\n");
} else {
Warning("\tdevice[%p]: Unable to get EXECUTION_CAPABILITIES: %s!\n",
device, CLErrString(status));
}
status = clGetDeviceInfo(device, CL_DEVICE_GLOBAL_MEM_CACHE_TYPE,
sizeof val, &val, NULL);
if (status == CL_SUCCESS) {
static const char *cacheTypes[] = { "None", "Read-Only", "Read-Write" };
static int numTypes = sizeof cacheTypes / sizeof cacheTypes[0];
printf("\tdevice[%p]: GLOBAL_MEM_CACHE_TYPE: %s (%lld)\n",
device, val < numTypes ? cacheTypes[val] : "???", val);
} else {
Warning("\tdevice[%p]: Unable to get GLOBAL_MEM_CACHE_TYPE: %s!\n",
device, CLErrString(status));
}
status = clGetDeviceInfo(device,
CL_DEVICE_LOCAL_MEM_TYPE, sizeof val, &val, NULL);
if (status == CL_SUCCESS) {
static const char *lmemTypes[] = { "???", "Local", "Global" };
static int numTypes = sizeof lmemTypes / sizeof lmemTypes[0];
printf("\tdevice[%p]: CL_DEVICE_LOCAL_MEM_TYPE: %s (%lld)\n",
device, val < numTypes ? lmemTypes[val] : "???", val);
} else {
Warning("\tdevice[%p]: Unable to get CL_DEVICE_LOCAL_MEM_TYPE: %s!\n",
device, CLErrString(status));
}
for (ii = 0; hexProps[ii].name != NULL; ii++) {
status = clGetDeviceInfo(device, hexProps[ii].param, sizeof val, &val, &size);
if (status != CL_SUCCESS) {
Warning("\tdevice[%p]: Unable to get %s: %s!\n",
device, hexProps[ii].name, CLErrString(status));
continue;
}
if (size > sizeof val) {
Warning("\tdevice[%p]: Large %s (%d bytes)! Truncating to %d!\n",
device, hexProps[ii].name, size, sizeof val);
}
printf("\tdevice[%p]: %s: 0x%llx\n",
device, hexProps[ii].name, val);
}
printf("\n");
for (ii = 0; longProps[ii].name != NULL; ii++) {
status = clGetDeviceInfo(device, longProps[ii].param, sizeof val, &val, &size);
if (status != CL_SUCCESS) {
Warning("\tdevice[%p]: Unable to get %s: %s!\n",
device, longProps[ii].name, CLErrString(status));
continue;
}
if (size > sizeof val) {
Warning("\tdevice[%p]: Large %s (%d bytes)! Truncating to %d!\n",
device, longProps[ii].name, size, sizeof val);
}
printf("\tdevice[%p]: %s: %lld\n",
device, longProps[ii].name, val);
}
}
/*
* PrintPlatform --
*
* Dumps everything about the given platform ID.
*
* Results:
* void.
*/
static void
PrintPlatform(cl_platform_id platform) {
static struct { cl_platform_info param; const char *name; } props[] = {
{ CL_PLATFORM_PROFILE, "profile" },
{ CL_PLATFORM_VERSION, "version" },
{ CL_PLATFORM_NAME, "name" },
{ CL_PLATFORM_VENDOR, "vendor" },
{ CL_PLATFORM_EXTENSIONS, "extensions" },
{ 0, NULL },
};
cl_device_id *deviceList;
cl_uint numDevices;
cl_int status;
char buf[65536];
size_t size;
int ii;
for (ii = 0; props[ii].name != NULL; ii++) {
status = clGetPlatformInfo(platform, props[ii].param, sizeof buf, buf, &size);
if (status != CL_SUCCESS) {
Warning("platform[%p]: Unable to get %s: %s\n",
platform, props[ii].name, CLErrString(status));
continue;
}
if (size > sizeof buf) {
Warning("platform[%p]: Huge %s (%d bytes)! Truncating to %d\n",
platform, props[ii].name, size, sizeof buf);
}
printf("platform[%p]: %s: %s\n", platform, props[ii].name, buf);
}
if ((status = clGetDeviceIDs(platform, CL_DEVICE_TYPE_ALL,
0, NULL, &numDevices)) != CL_SUCCESS) {
Warning("platform[%p]: Unable to query the number of devices: %s\n",
platform, CLErrString(status));
return;
}
printf("platform[%p]: Found %d device(s).\n", platform, numDevices);
deviceList = (cl_device_id *)malloc(numDevices * sizeof(cl_device_id));
if ((status = clGetDeviceIDs(platform, CL_DEVICE_TYPE_ALL,
numDevices, deviceList, NULL)) != CL_SUCCESS) {
Warning("platform[%p]: Unable to enumerate the devices: %s\n",
platform, CLErrString(status));
free(deviceList);
return;
}
for (ii = 0; ii < numDevices; ii++) {
PrintDevice(deviceList[ii]);
}
free(deviceList);
}
int main(int argc, char** argv)
{
int err; // error code returned from api calls
float data[DATA_SIZE]; // original data set given to device
float results[DATA_SIZE]; // results returned from device
unsigned int correct; // number of correct results returned
size_t global; // global domain size for our calculation
size_t local; // local domain size for our calculation
cl_platform_id platform; // compute platform id
cl_uint numPlatforms;
cl_platform_id *platformList;
cl_int status;
cl_device_id device_id; // compute device id
cl_context context; // compute context
cl_command_queue commands; // compute command queue
cl_program program; // compute program
cl_kernel kernel; // compute kernel
cl_mem input; // device memory used for the input array
cl_mem output; // device memory used for the output array
// Fill our data set with random float values
//
int i = 0;
unsigned int count = DATA_SIZE;
for(i = 0; i < count; i++)
{
data[i] = rand() / (float)RAND_MAX;
// printf("%f\n",data[i]);
}
err = clGetPlatformIDs(1, &platform, &numPlatforms);
if(err < 0) {
perror("Couldn't find any platforms");
return EXIT_FAILURE;
}
printf("Found %d platform(s).\n", numPlatforms);
platformList = (cl_platform_id *) malloc(sizeof(cl_platform_id) * numPlatforms);
if ((status = clGetPlatformIDs(numPlatforms, platformList, NULL)) != CL_SUCCESS) {
Warning("Unable to enumerate the platforms: %s\n",
CLErrString(status));
exit(1);
}
int ii;
for (ii = 0; ii < numPlatforms; ii++) {
PrintPlatform(platformList[ii]);
}
// Connect to a compute device
//
int gpu = 1;
err = clGetDeviceIDs(platformList[0], gpu ? CL_DEVICE_TYPE_GPU : CL_DEVICE_TYPE_CPU, 1, &device_id, NULL);
if (err != CL_SUCCESS)
{
printf("Error: Failed to create a device group!\n");
return EXIT_FAILURE;
}
// Create a compute context
//
context = clCreateContext(0, 1, &device_id, NULL, NULL, &err);
if (!context)
{
printf("Error: Failed to create a compute context!\n");
return EXIT_FAILURE;
}
// Create a command commands
//
commands = clCreateCommandQueue(context, device_id, 0, &err);
if (!commands)
{
printf("Error: Failed to create a command commands!\n");
return EXIT_FAILURE;
}
// Create the compute program from the source buffer
//
program = clCreateProgramWithSource(context, 1, (const char **) & KernelSource, NULL, &err);
if (!program)
{
printf("Error: Failed to create compute program!\n");
return EXIT_FAILURE;
}
// Build the program executable
//
err = clBuildProgram(program, 0, NULL, NULL, NULL, NULL);
if (err != CL_SUCCESS)
{
size_t len;
char buffer[2048];
printf("Error: Failed to build program executable!\n");
clGetProgramBuildInfo(program, device_id, CL_PROGRAM_BUILD_LOG, sizeof(buffer), buffer, &len);
printf("%s\n", buffer);
exit(1);
}
// Create the compute kernel in the program we wish to run
//
kernel = clCreateKernel(program, "square", &err);
if (!kernel || err != CL_SUCCESS)
{
printf("Error: Failed to create compute kernel!\n");
exit(1);
}
// Create the input and output arrays in device memory for our calculation
//
input = clCreateBuffer(context, CL_MEM_READ_ONLY, sizeof(float) * count, NULL, NULL);
output = clCreateBuffer(context, CL_MEM_WRITE_ONLY, sizeof(float) * count, NULL, NULL);
if (!input || !output)
{
printf("Error: Failed to allocate device memory!\n");
exit(1);
}
// Write our data set into the input array in device memory
//
err = clEnqueueWriteBuffer(commands, input, CL_TRUE, 0, sizeof(float) * count, data, 0, NULL, NULL);
if (err != CL_SUCCESS)
{
printf("Error: Failed to write to source array!\n");
exit(1);
}
// Set the arguments to our compute kernel
//
err = 0;
err = clSetKernelArg(kernel, 0, sizeof(cl_mem), &input);
err |= clSetKernelArg(kernel, 1, sizeof(cl_mem), &output);
err |= clSetKernelArg(kernel, 2, sizeof(unsigned int), &count);
if (err != CL_SUCCESS)
{
printf("Error: Failed to set kernel arguments! %d\n", err);
exit(1);
}
// Get the maximum work group size for executing the kernel on the device
//
err = clGetKernelWorkGroupInfo(kernel, device_id, CL_KERNEL_WORK_GROUP_SIZE, sizeof(local), &local, NULL);
if (err != CL_SUCCESS)
{
printf("Error: Failed to retrieve kernel work group info! %d\n", err);
exit(1);
}
// Execute the kernel over the entire range of our 1d input data set
// using the maximum number of work group items for this device
//
global = count;
err = clEnqueueNDRangeKernel(commands, kernel, 1, NULL, &global, &local, 0, NULL, NULL);
if (err)
{
printf("Error: Failed to execute kernel!\n");
return EXIT_FAILURE;
}
// Wait for the command commands to get serviced before reading back results
//
clFinish(commands);
// Read back the results from the device to verify the output
//
err = clEnqueueReadBuffer( commands, output, CL_TRUE, 0, sizeof(float) * count, results, 0, NULL, NULL );
if (err != CL_SUCCESS)
{
printf("Error: Failed to read output array! %d\n", err);
exit(1);
}
// Validate our results
//
correct = 0;
for(i = 0; i < count; i++)
{
//printf("%4f %4.10f %4.10f \n", data[i],data[i] * data[i], results[i]);
if((results[i] - data[i] * data[i]) < 10e-8)
correct++;
}
// Print a brief summary detailing the results
//
printf("Computed '%d/%d' correct values!\n", correct, count);
// Shutdown and cleanup
//
free(platformList);
clReleaseMemObject(input);
clReleaseMemObject(output);
clReleaseProgram(program);
clReleaseKernel(kernel);
clReleaseCommandQueue(commands);
clReleaseContext(context);
return 0;
}
我在Geforce 8800 GTS上运行。
F:\Documents\Dropbox\05030 - OpenCL\Samples\Debug>HelloWorld.exe
Found 1 platform(s).
platform[012C6F88]: profile: FULL_PROFILE
platform[012C6F88]: version: OpenCL 1.1 CUDA 4.2.1
platform[012C6F88]: name: NVIDIA CUDA
platform[012C6F88]: vendor: NVIDIA Corporation
platform[012C6F88]: extensions: cl_khr_byte_addressable_store cl_khr_icd cl_khr_
gl_sharing cl_nv_d3d9_sharing cl_nv_d3d10_sharing cl_khr_d3d10_sharing cl_nv_d3d
11_sharing cl_nv_compiler_options cl_nv_device_attribute_query cl_nv_pragma_unro
ll
platform[012C6F88]: Found 1 device(s).
device[012C6FF0]: NAME: GeForce 8800 GTS
device[012C6FF0]: VENDOR: NVIDIA Corporation
device[012C6FF0]: PROFILE: FULL_PROFILE
device[012C6FF0]: VERSION: OpenCL 1.0 CUDA
device[012C6FF0]: EXTENSIONS: cl_khr_byte_addressable_store cl_khr_icd c
l_khr_gl_sharing cl_nv_d3d9_sharing cl_nv_d3d10_sharing cl_khr_d3d10_sharing cl_
nv_d3d11_sharing cl_nv_compiler_options cl_nv_device_attribute_query cl_nv_pragm
a_unroll
device[012C6FF0]: DRIVER_VERSION: 301.42
device[012C6FF0]: Type: GPU
device[012C6FF0]: EXECUTION_CAPABILITIES: Kernel
device[012C6FF0]: GLOBAL_MEM_CACHE_TYPE: None (0)
device[012C6FF0]: CL_DEVICE_LOCAL_MEM_TYPE: Local (1)
device[012C6FF0]: SINGLE_FP_CONFIG: 0x3e
device[012C6FF0]: QUEUE_PROPERTIES: 0x3
device[012C6FF0]: VENDOR_ID: 4318
device[012C6FF0]: MAX_COMPUTE_UNITS: 12
device[012C6FF0]: MAX_WORK_ITEM_DIMENSIONS: 3
device[012C6FF0]: MAX_WORK_GROUP_SIZE: 512
device[012C6FF0]: PREFERRED_VECTOR_WIDTH_CHAR: 1
device[012C6FF0]: PREFERRED_VECTOR_WIDTH_SHORT: 1
device[012C6FF0]: PREFERRED_VECTOR_WIDTH_INT: 1
device[012C6FF0]: PREFERRED_VECTOR_WIDTH_LONG: 1
device[012C6FF0]: PREFERRED_VECTOR_WIDTH_FLOAT: 1
device[012C6FF0]: PREFERRED_VECTOR_WIDTH_DOUBLE: 0
device[012C6FF0]: MAX_CLOCK_FREQUENCY: 1188
device[012C6FF0]: ADDRESS_BITS: 32
device[012C6FF0]: MAX_MEM_ALLOC_SIZE: 134217728
device[012C6FF0]: IMAGE_SUPPORT: 1
device[012C6FF0]: MAX_READ_IMAGE_ARGS: 128
device[012C6FF0]: MAX_WRITE_IMAGE_ARGS: 8
device[012C6FF0]: IMAGE2D_MAX_WIDTH: 4096
device[012C6FF0]: IMAGE2D_MAX_HEIGHT: 16383
device[012C6FF0]: IMAGE3D_MAX_WIDTH: 2048
device[012C6FF0]: IMAGE3D_MAX_HEIGHT: 2048
device[012C6FF0]: IMAGE3D_MAX_DEPTH: 2048
device[012C6FF0]: MAX_SAMPLERS: 16
device[012C6FF0]: MAX_PARAMETER_SIZE: 4352
device[012C6FF0]: MEM_BASE_ADDR_ALIGN: 2048
device[012C6FF0]: MIN_DATA_TYPE_ALIGN_SIZE: 128
device[012C6FF0]: GLOBAL_MEM_CACHELINE_SIZE: 0
device[012C6FF0]: GLOBAL_MEM_CACHE_SIZE: 0
device[012C6FF0]: GLOBAL_MEM_SIZE: 335544320
device[012C6FF0]: MAX_CONSTANT_BUFFER_SIZE: 65536
device[012C6FF0]: MAX_CONSTANT_ARGS: 9
device[012C6FF0]: LOCAL_MEM_SIZE: 16384
device[012C6FF0]: ERROR_CORRECTION_SUPPORT: 0
device[012C6FF0]: PROFILING_TIMER_RESOLUTION: 1000
device[012C6FF0]: ENDIAN_LITTLE: 1
device[012C6FF0]: AVAILABLE: 1
device[012C6FF0]: COMPILER_AVAILABLE: 1
hello world示例的结果是：计算'0/1024'正确值！ 改变abit，比如结果
result[i] == data[i]*data[i]
但
(result[i] - data[i]*data[i] ) < 10e-6
我得到的所有价值都是正确的。我现在想知道原因。所有数据都存储在主机上：
float data[DATA_SIZE]; // original data set given to device
float results[DATA_SIZE]; // results returned from device
我正在使用visual studio 2010进行编译，并想知道如何评估两个浮动a == b，它需要具有多大的精度。
我应该总是假设我的GPU上的计算是正确的差异＆lt; 10e-8？新卡会有不同之处吗？我订购了HD 7970。
最后，如果有人有一些非常好的入门指南，我很感兴趣。
答案 0 :(得分：0)
没有绝对值可用于比较在所有情况下都适用的两个浮点数（任何精度）。原因在于，由于表示，两个“相邻”浮点数可以具有大的绝对差。更好的方法是使用相对误差进行比较（相对误差：abs((a-b)/b)） - 虽然这只是一种粗略的方法，但也需要考虑一些边缘情况。
答案 1 :(得分：0)
这是一个问题的答案。
总结：当执行中间操作时，cpu存储比浮点（32位）更高位（80位）精度的值，因为[i]＆lt;在[I] * [I]中。
答案 2 :(得分：0)
当：
result[i] == data[i]*data[i]
你有数据[i] * data [i]计算，然后存储在某处（临时变量，寄存器），然后与result [i]
进行比较当：
result[i] - data[i]*data[i]
你有数据[i]加载，乘以它自己，然后减去结果[i]
在第一种情况下，比较两个存储的浮点变量 在第二种情况下，从存储的浮点数（具有固定的4字节表示）中减去中间计算结果（使用存储表示的更多数字完成）。
您可能会在普通cpu C ++代码中得到相同的错误结果（可能因编译器/ CPU而异）。 使用硬件精度，公式中的任何中间结果都可以具有比数据类型更重要的数字，以便仅在存储结果时进行舍入。它提高了精度。
如果你想比较两者，请执行：
float a = result[i];
float b = data[i]*data[i];
float delta = a-b; // should be 0.0
通常情况下，好的做法是永远不要使用相等（a == b）来比较浮动值，因为这个帖子的大小有太多原因。
在您的情况下，它是合法的（检查GPU和CPU上的精度/舍入是否相同），但只能比较存储的值